Most of the insects belonging to this tribe are parasitic on other
insects. The _larvæ_ are footless. There are seven families included in
the _Entomophaga_.
[Illustration: Fig. 29.--Cynips Gallæ Tinctoriæ (Mag.)]
_Family 18, Cynipidæ._--This family includes most of the gall flies.
The number of species is very considerable. Of the great majority the
females pierce with their ovipositor the tissues of plants and trees,
and there deposit their eggs, from which the _larvæ_ are soon hatched.
The irritation caused by this intrusion of a foreign body into the
tissues produces the galls which are so commonly met with.
[Illustration: Fig. 30.--Smicra Sispes (Mag.)]
The galls produced by different species of flies differ greatly in form
and structure. Some of them are round and smooth, like fruits, such as
the cherry gall of the oak leaves, produced by the puncture of _Cynips
quercus-foli_.
The most singular, however, of all the galls is perhaps the Bedeguar,
which is formed on the stems of wild roses by the puncture of a small
species, _Rhodites rosæ_.
_Family 19, Chalcididæ._--To this family belong many gall insects,
principally found, however, in foreign countries.
The _Chalcididæ_ include a great number of small species, few exceeding
half an inch in expanse. Many of these are singular in shape, and
others brilliantly metallic; but, owing to their small size, they have
hitherto been studied by comparatively few entomologists.
[Illustration: Fig. 31.--Thoracamba Furcata (Mag.)]
_Family 20, Proctotrypidæ._--The _Proctotrypidæ_ are probably much less
numerous than the preceding family, but have been less studied, being
generally smaller and more obscure in their habits; in fact, some of
them share with several beetles the reputation of being the smallest
insects.
[Illustration: Fig. 32.--Proctotrypes Rufipes (Mag.)]
_Family 21, Braconidæ._--This family is one of very great extent.
Many of the foreign species are rather large and handsome insects,
often varied with black and yellow.
The best known of the _Braconidæ_ is perhaps _Microgaster glomeratus_,
a small blackish species with reddish-yellow legs, which destroys the
_larvæ_ of the common Cabbage Butterflies, round the dead body of which
its little yellow cocoons may often be observed.
_Family 22, Ichneumonidæ._--The _Ichneumonidæ_ are rather large and
slender insects, and are divided into many sub-families.
[Illustration: Fig. 33.--Bracon Bicolor.]
They are a very numerous group. It has been calculated that nearly
5,000 species have been described, but the data generally are very
untrustworthy.
[Illustration: Fig. 34.--Joppa Antennata.]
The species of _Trogus_ are rather large insects, measuring an inch or
more in length. They are black with reddish legs and abdomen, and the
wings are sometimes slightly dusky at the edges.
[Illustration: Fig. 35.--Evania Appendigaster (Mag.)]
[Illustration: Fig. 36.--Pelecinus Politurator.]
In another group, _Pimplinæ_, the ovipositor is generally very long.
The best-known species is _Rhyssa persuasoria_, a blackish insect,
which measures about an inch in length. This insect is met with in
fir plantations, and uses its extraordinary ovipositor to drill holes
in trees infested by the _larvæ_ of _Sirex gigas_, on which its own
_larva_ is parasitic. The insect frequently drives its ovipositor so
firmly into the wood of the tree, that it is unable to withdraw it, and
perishes in this position.
_Family 23, Evaniidæ._--One of the most familiar insects belonging to
this family is the _Evania appendigaster_. It is a small black insect,
found in the south of Europe, and is parasitic on cockroaches. An
allied British species, _Fœnus jaculator_, is a not uncommon insect
found haunting the burrows of _Crabronidæ_, upon which it is probably
parasitic.
_Family 24, Chrysididæ._--The Ruby-tailed Wasps, or Golden Wasps, as
the _Chrysididæ_ are popularly called, are among the most brilliant
of the _Hymenoptera_, most of the species being either of an intense
green, blue, or fiery red.
They are small or moderate-sized insects, which are found on walls
or flowers in the full heat of the sun; for, as a rule, the most
brilliantly-coloured insects are diurnal in their habits.
[Illustration: Fig. 37.--Chrysis Ignita (Mag.)]
As far as their habits are known, they deposit their eggs in the nests
of other insects, chiefly _Hymenoptera_, on the _larvæ_ of which their
own offspring feed.
The commonest British species is _Chrysis ignita_, which is a very
variable insect, both as regards size and colouring.